1. Field of the Invention
The present invention relates to a lens apparatus (or a lens barrel) and an optical apparatus equipped with the same, which are suitably applied to optical apparatuses such as still cameras, digital still cameras and video cameras.
2. Related Background Art
Various lens barrels of the collapsible type have been conventionally proposed. In the collapsible type lens barrel, a lens barrel member such as a lens holding frame that holds a lens(es) is moved toward the camera body to reduce its length along the optical axis to thereby improve portability.
Japanese Patent Application Laid-Open No. 2001-324663 discloses a mechanism, used in a lens barrel of the collapsible type, that drives a focusing lens (the third lens unit) along the optical axis direction while effecting position control. This mechanism is adapted to drive the focusing lens by rotating an output screw portion of a stepping motor mounted on a base member on which an image pickup element is held while regulating the position of a lens barrel member that fixedly holds the focusing lens along the optical axis by engagement of the output screw portion of the stepping motor and a nut portion provided on the lens barrel member for the focusing lens.
In addition, the initial position of the lens barrel member for the third lens unit is determined by passing of a projection formed on the lens barrel member through a photosensor, and position control along the optical axis is effected by driving the rotation of the stepping motor from the initial position using pulses.
In the lens apparatus disclosed in Japanese Patent Application Laid-Open No. 2001-324663, the output screw portion of the stepping motor for driving the lens barrel member for the third lens unit and the nut portion provided on the lens barrel member are disposed inside a cam ring. Accordingly, there is a risk that these portions can interfere with the lens barrel member of the magnification changing lens (or the first and second lens units) driven along the optical axis by the cam ring, and therefore it is difficult to reduce the total length of the lens in the collapsed state.
According to one method of preventing the interfere, an opening is formed on the lens barrel member for the magnification changing lens to prevent its interference with the output screw portion of the stepping motor. However, this method sometimes invites entrance of undesirable light onto the image pickup element through the opening.
Japanese Patent Application Laid-Open No. 2003-131111 also discloses a lens driving mechanism. In this mechanism, in the collapsed state in which image taking is not allowed, the first and second lens units are moved backward along the optical axis so as to be kept in the collapsed position.
In this collapsible lens barrel, a drive source for focusing composed of a stepping motor for driving the third lens unit is provided outside the first lens unit and the second lens unit.
In the lens apparatus disclosed in Japanese Patent Application Laid-Open No. 2003-131111, the sum of the length of the stepping motor and the length of the output screw portion is significantly long as compared to the move amount of the lens units along the optical axis. Accordingly, it is difficult to make the length of the lens barrel short, and it is disadvantageous in terms of portability.
Furthermore, in the case that driving of focusing lens is controlled by an operation of the stepping motor with pulses as is the case with the above-mentioned patent documents, it is difficult to achieve fine movement and high speed, since the movement pitch of the focusing lens is determined by the pitch of the screw of the stepping motor.